In recent years, as the line capacity of the Internet has increased and the element technique of handling versatile media information has been provided, people have come to enjoy information delivery by rich media from mobile terminals at any time anywhere. Such a lifestyle has been widely penetrated, and as a high-speed mobile environment for supporting the information delivery, a communication environment such as LTE (Long Term Evolution) and the like is being spread and expanded.
In the high-speed mobile communication environment such as LTE and the like, a variety of techniques for enhancing data communication efficiency are introduced in a protocol of each layer. For example, in an RLC (Radio Link Control) layer in LTE, in order to reduce redundant fragments and overheads, the transmitter divides and links data transferred from an upper layer, and the receiver restores the data by performing sequence control and transfers the data to the upper layer so as to use up each service data unit.
Further, in a MAC (Media Access Control) layer in LTE or in HSDPA (High Speed Downlink Packet Access), an HARQ (Hybrid Automatic Repeat reQuest) technique of efficiently correcting a communication data error is introduced by making data redundant in advance in a wireless network in which a bit error is likely to occur, and by re-transmitting the redundant portion by one-eighth each when a bit error occurs. According to the HARQ technique, it is possible to complete data re-transmission and restoration processing in the MAC layer or lower, and to reduce an amount of data to be re-transmitted, and thus, it is possible to realize effective use of a wireless band.
According to the data dividing and linking processing in the high-speed mobile communication environment or the HARQ technique, described above, it is possible to virtually provide a network with less overheads and errors in terms of a protocol of an upper layer (it is possible to simultaneously reduce an error in terms of a protocol of an upper layer).
However, since a content of the technique is that a bit error is restored by re-transmission, there is a problem that delay occurs in terms of a protocol of an upper layer.
Further, in TCP (Transmission Control Protocol) conventionally and widely used in both of wired and wireless data communication, a technique for congestion control has been advanced in order to cope with a recent communication environment in which many pieces of traffic co-exist.
In association with the above, in delay-based TCP as represented by TCP Vegas (NPL 1) and FAST TCP (NPL 2), it is possible to suppress a data transmission rate before a packet loss occurs by detecting congestion through analysis of a situation regarding increase in delay. This makes it possible to stabilize throughput while escaping failure of a network.
However, in delay-based TCP disclosed in NPL 1 or NPL 2 described above, when a product of an available bandwidth and an amount of increase in delay exceeds a predetermined threshold value, due to determining that the network is in a congestion state, and performing control that a data transmission rate is lowered, a problem occurs that a transmission rate is unnecessarily lowered by recognizing by mistake that congestion occurs even when the increase in delay is not caused by congestion.
As a related technique in view of the aforementioned problem, for example, the following contents of techniques (PTL 1 or PTL 2) are known.
PTL 1 discloses a content of a technique, in which, when a burst-type packet loss occurs during streaming, it is determined that the packet loss is caused by a link failure (a failure such as cutoff of a communication link by breaking of an optical fiber or the like) or a node failure (a failure due to breakdown of equipment such as a router, abnormality of a router configuration, or the like), and a stream transmission rate is maintained by using stored network statistical information in the past, in place of the current network statistical information.
PTL 2 discloses a content of a technique, in which, it is determined whether or not to be in a congestion state and whether or not to be a transmission error by analysis of feedback data, and when both being in a congestion state and being a transmission error are determined, it is judged that congestion does not occur, and delivery is continued without changing the transfer rate.